Split SetFixedSize and SetDirectionTriggersScrollbar in multiple functions.

This is a follow up patch that fixes https://codereview.chromium.org/2446243003/#msg11 comment and a couple of compiler warnings about unitialized values.

BUG=635619

Review-Url: https://codereview.chromium.org/2451223003
Cr-Commit-Position: refs/heads/master@{#427920}
2 files changed